Coupling a drive motor to a cassette reel can be problematic as a result of radial, axial, or angular misalignment between the drive motor output shaft and the cassette reel axle. One option in addressing this problem is to use a data cartridge which incorporates a drive belt. This solution generally only solves the radial misalignment problem. Another option, which is used in all audio and video cassette systems, is to allow the tape reel to float inside the cartridge. The tape reels in such systems do not rotate on axes that are rigidly attached to the cartridge. The reels can move within a certain range to align with the drive axes. Usually, the engagement method has some kind of self-centering device, such as multi-toothed couplings, or the reel is allowed a certain amount of wobble. A third option is to have the tape reels rotate on axes that are rigidly connected to the cassette housing, and allow the driveshaft axes to adjust to the cassette reels. The advantage of this kind of system is that a precision tape path can be defined entirely within the cassette for excellent guiding, low debris generation, etc. In this option, each reel includes an axle with a bearing that is designed to have a close fit, however, the axle will rock slightly if the tape driving mechanism is not aligned with it. This rocking motion results in an unreliable tape path which can cause low quality recording or playing of the tape.
Referring to FIGS. 1--3, an apparatus 10 for driving a tape reel is shown in accordance with a prior art embodiment. The tape drive apparatus 10 includes a multi-toothed coupling 12 which is connected to an output shaft 14 of a motor 16. The output shaft 14 has an axis of rotation 18. The tape reel includes a multi-toothed coupling 20 and is mounted for rotation about an axis 22 by an axle 24 which is connected to a cassette housing 26. As shown in FIG. 1, the motor shaft axis 18 and reel axis 24 are radially misaligned. This will cause the multi-toothed couplings 12,20 to improperly mesh, which will result in rocking of the tape reel 28 on the axis 22 and undue wear between the gears.
Turning to FIG. 2, another meshing problem is illustrated. In this Figure, it is shown that the multi-toothed couplings 12,20 are axially misaligned, in that the multi-toothed couplings are undesirably too far apart. This axial misalignment creates difficulty in multi-toothed coupling meshing.
Turning to FIG. 3, another problem associated with prior art tape drive assemblies is illustrated in that the axes 18 and 22 are angularly misaligned, which will lead to improper multi-toothed coupling meshing, which may lead to backlash and other quality problems.
The typical off-center drive problem is addressed in various art areas by mechanical devices, such as universal joints in automobiles, elastic joints in heavy machinery, and bellows couplings or Oldham couplings in precision equipment. None of these prior art devices provide the high torsional stiffness and low axial deflection stiffness required in a tape drive assembly while being capable of supporting a thrust load. The high torsional stiffness is required to rotate the cassette reel and the low axial deflection stiffness is required to prevent the exertion of a tipping torque on the reel axle. Large tipping torques can result in rocking of the reel.
U.S. Pat. No. 5,490,020 to IBM teaches one effort to overcome the above-referenced problem experienced with prior art assemblies. In effect, this design incorporates a version of a universal joint used in cooperation with a telescoping joint for addressing the radial and axial misalignment problems. However, this assembly is very complex and expensive to manufacture, and it exhibits undesirable backlash and the torsional stiffness is too low. Also, the design is very tall, so it consumes substantial space.